NEW YORK— Police say an 18-year-old man attacked two fellow students inside a New York City school, fatally stabbing a 15-year-old boy and critically injuring a 16-year-old boy.

The attack happened Wednesday on the fifth floor of the Urban Assembly School for Wildlife Conservation, a middle and high school in the Bronx. It's located in a building that also houses a public elementary school.

Police say the 18-year-old has been taken into custody, but it's not yet clear what prompted the attack.

According to WPIX, a preliminary investigation indicated bullying may have prompted the attack, sources said.

Schools Chancellor Carmen Fariña has responded to the deadly incident:

“I’m heartbroken at the loss of one of our students and this tragedy should never have taken place. We are working closely with the NYPD on the investigation and providing ongoing guidance support and counseling for the school community.”

Police didn't immediately say what type of cutting device was used, but a weapon was recovered.